SHMFF水冷系统蓄水罐与冷水机组联合供冷模式研究

稳态强磁场实验装置水冷系统具有大流量、大蓄冷温差的特性。前期设计由于考虑占地、成本等因素,所具备的蓄冷量无法满足今后磁体实验延长实验时间的要求。为扩大蓄冷量,提高冷冻水使用效率,现提出了蓄冷罐联合冷水机组供冷的模式,并将其与自然分层法进行了对比分析。     

Application of radiation modes to the problem of low-frequency noise from a highway bridge

Low-frequency noise radiated from highway bridges is a serious environmental problem in Japan. Although the suppression of bridge vibration as usually done in practice can alleviate the radiation, it may not be optimal because the behavior of radiation is not taken into consideration. Concept of radiation modes, which can represent both vibration and radiation behavior, is adapted to a highway bridge. The objectives of this paper are to study the benefits of using radiation modes in (1) identification of low-frequency noise characteristics and (2) active control of low-frequency noise radiation. Numerical study shows that the radiation modes enable radiation characteristics of low-frequency noise to be physically understood and the active controller designed by radiation modes is superior to the controller designed without considering radiation behavior. Because the concept of radiation modes can reveal the mechanics of radiation/vibration, it is appropriate to the problem of low-frequency noise radiated from highway bridges.     

结构振动模态之间耦合对预测结构声功率的影响

以简支矩形板为例,分析结构振动模态之间的耦合对声功率的影响。通过对声功率传递矩阵计算方法的改进,得到计算声功率传递矩阵对角元素和非对角元素(模态耦合项)的解析解,并进行数值计算和分析。所得解析解结果同前人发表的数值解非常吻合。     

超临界Lennard-Jones流体结构特性分子动力学研究

研究超临界流体在不同压力和温度的结构特征有助于深刻理解并有效利用超临界流体.本文采用分子动力学方法模拟超临界压力、拟临界温度附近流体的结构及密度波动曲线的排列熵,分析状态参数变化的影响.结果表明,定压下,径向分布函数随温度升高,第一峰值位置逐渐向右移动,但右移幅度随着压力偏离临界点距离的增大而减弱,近临界压力时,出现峰值最高点的工况和等温压缩系数的极值点位置一致,压力增大,该现象消失.低压力拟临界点时易出现面积大、相对集中且分布稳定的高/低密度区,无明显嵌套现象.静态结构因子存在一定发散行为,发散的最大值和等温压缩系数极值点所处工况符合.低压力时密度时间序列的波动幅度最大,类周期现象较明显.在分子间势能、等温压缩系数和热运动效应的共同作用下,当压力(P)为1.1倍的临界压力(Pc)时,排列熵在0.99倍的拟临界温度(Tpc)达到最小值,P = 1.3Pc和1.5Pc时,最小排列熵与等温压缩系数的最大值工况点保持一致,压力继续增大,各模拟工况密度和排列熵的波动减弱,流体均匀性增强.     

Experimental study of the influence of annular nozzle on acoustic characteristics of detonation sound wave generated by pulse detonation engine

Acoustic characteristics of the detonation sound wave generated by a pulse detonation engine with an annular nozzle, including peak sound pressure, directivity, and A duration, are experimentally investigated while utilizing gasoline as fuel and oxygen-enriched air as oxidizer. Three annular nozzle geometries are evaluated by varying the ratio of inner cone diameter to detonation tube exit diameter from 0.36 to 0.68. The experimental results show that the annular nozzles have a significant effect on the acoustic characteristics of the detonation sound wave. The annular nozzles can amplify the peak sound pressure of the detonation sound wave at 90° while reducing it at 0° and 30°. The directivity angle of the detonation sound wave is changed by annular nozzles from 30° to 90°. The A duration of the detonation sound wave at 90° is also increased by the annular nozzles. These changes indicate that the annular nozzles have an important influence on the acoustic energy distribution of the detonation sound wave, which amplify the acoustic energy in a direction perpendicular to the tube axis and weaken it along the direction of the tube axis.     

多管PDE爆轰噪声传播过程物理特性实验研究

为研究多管脉冲爆轰发动机爆轰噪声传播过程及声波物理特性,对单管至四管脉冲爆轰发动机爆轰噪声物理特性开展实验研究,获得了多管脉冲爆轰发动机爆轰噪声的波形、声压衰减规律、辐射特性、持续时间和频谱特性等物理参数。结果表明:在管口区域,爆轰噪声峰值衰减较快,在远离管口区域,衰减速率逐渐放缓。随着爆轰管数量的增加,爆轰峰值噪声在各方位角上的声压级逐渐增大。在远场区域内爆轰噪声指向性图呈“M”形。随着爆轰管数量的增加,爆轰噪声的A/B持续时间均增加。爆轰噪声是能量主要集中在中低频段的宽频噪声,其频谱峰值和峰值所在频点随爆轰管数量的增加而改变。     

石墨烯纳米孔道内受限水介电常数影响因素的分子动力学模拟

受限水的介电特性对于石墨烯电容器的储能效率有着重大的影响.因此本文使用分子动力模方法,研究了不同石墨烯纳米孔道宽度(0.812～10 nm)下内受限水介电常数的分布及其影响因素.结果表明,在石墨烯纳米孔道内部受限水双电层结构可分为空隙层、界面层和体相层三个部分.其整体的介电常数随孔道大小的降低而线性减少.这是由内部体相层的宽度的降低而导致的.此外电极电压大小和石墨烯-水相互作用参数ε_CO的强弱也会显著改变电极表面的双电层(Electric Double Layers, EDLs)结构.其中电压的增大使得介电常数分布的震荡的程度也随之增加,最终导致了整体介电常数的减小.与之类似,亲水态的石墨烯表面(高ε_CO)下受限水分布的震荡程度也显著增加,这导致了整体介电常数的降低.     

Development and study of novel non-contact ultrasonic motor based on principle of structural asymmetry

The article presents novel design of non-contact rotary ultrasonic motor consisting of ring-shaped stator vibrating in in-plane flexural mode and rotor provided with blades. In contrast to other motors with similar design proposed motor relies on the use of standing ultrasonic waves. This simplifies design and electronic control of motor and becomes possible due to introduction of artificial asymmetry, for example by tilting one or several blades of the rotor relative to the surface normal. Operating principle of the proposed motor is based on acoustic radiation torque exerted on rotor by ultrasonic waves propagating in air or fluid gap between rotor and stator. This torque is calculated using finite element method by means of COMSOL Multiphysics software. Dynamics of rotor is studied using MathCad software and general theory of nonlinear conservative oscillators. Role of asymmetry is explained on the basis of comparative analysis of potential functions and phase trajectories for symmetric and asymmetric cases. It is shown that direction of rotation is determined by structural parameters of motor, particularly tilting direction (clockwise or counter-clockwise) of the blades. Conceptual design of motor with bidirectional rotation is described. Direction and velocity of rotation in the proposed conceptual design can be potentially controlled by changing excitation frequency of stator.     

The influence of flow on the acoustic characteristics of a duct bend for higher order modes—A numerical study

A numerical technique was used to investigate the effects of flow on the acoustic transmission and reflection characteristics of a duct bend. The range of wave numbers examined extended to the cut-on value of the second cross-mode. Characteristics were studied in terms of the velocity potential, the acoustic pressure and the energy flux. The effects of locating a turning vane centrally in the bend were also examined in terms of the energy flux.     

A study of the structural and spectral characteristics of free and bound water in kaolinite

The dependence of the Si–O stretching vibration line intensity in the IR spectrum of kaolinite on the humidity of this mineral has been experimentally investigated. The experimental data were interpreted on the basis of density functional theory (DFT) calculations with allowance for the real crystallographic features of the kaolinite sample, determined by structural analysis. Some specific features of the intensity behavior in the plastic state are revealed, which can be used to develop techniques for determining its limits. The differences in the O–H bond lengths and H–O–H angles for the H₂O molecules adsorbed by basal surfaces and located in the porous space of the mineral are determined. Based on the DFT data, it was found that bond lengths and bond angles for a water molecule adsorbed on the siloxane surface are systematically smaller than for a water molecule adsorbed on the hydroxyl surface.     

基于声辐射模态的有源控制解耦在固定支承板上的研究

基于声辐射模态的主动控制理论,以固定支承板为例,通过四组作动器在固定支承板上的布放,使其能分别控制不同阶声辐射模态辐射的声功率,来使控制方程解耦,从而设计了比较简单与稳定的单输入/单输出控制系统,模拟计算取得了较好的控制效果。同时本文对控制过程中的溢出等问题进行了一定的探讨。     

A classical molecular dynamics study of a Diels Alder cycloaddition in supercritical water

Molecular dynamics simulations were performed to investigate the Diels Alder cycloaddition of cyclopentadiene and methyl vinyl ketone in high pressure, high temperature water. It was found that the reaction was favoured by high temperatures at 1000?atm due to increasing entropy. Similarly, at 400?atm, the entropy caused both the equilibrium and rate constant to increase to a peak at 698?K before rapidly falling once more with increasing temperature. At a constant temperature of either 598?K or 898?K, increasing pressure resulted in a lowering of the equilibrium constant. This effect was significantly more pronounced for 898?K, caused by less favourable solvation of the products and an increasing amount of work required for reaction.     

High-temperature dynamic behavior in bulk liquid water: A molecular dynamics simulation study using the OPC and TIP4P-Ew potentials

Classical molecular dynamics simulations were performed to study the high-temperature (above 300 K) dynamic behavior of bulk water, specifically the behavior of the diffusion coefficient, hydrogen bond, and nearest-neighbor lifetimes. Two water potentials were compared: the recently proposed “globally optimal” point charge (OPC) model and the well-known TIP4P-Ew model. By considering the Arrhenius plots of the computed inverse diffusion coefficient and rotational relaxation constants, a crossover from Vogel–Fulcher–Tammann behavior to a linear trend with increasing temperature was detected at T* ≈ 309 and T* ≈ 285 K for the OPC and TIP4P-Ew models, respectively. Experimentally, the crossover point was previously observed at T* ± 315–5 K. We also verified that for the coefficient of thermal expansion α _P (T, P), the isobaric α _P (T) curves cross at about the same T* as in the experiment. The lifetimes of water hydrogen bonds and of the nearest neighbors were evaluated and were found to cross near T*, where the lifetimes are about 1 ps. For T < T*, hydrogen bonds persist longer than nearest neighbors, suggesting that the hydrogen bonding network dominates the water structure at T < T*, whereas for T > T*, water behaves more like a simple liquid. The fact that T* falls within the biologically relevant temperature range is a strong motivation for further analysis of the phenomenon and its possible consequences for biomolecular systems.     

Effect of size polydispersity on the structural and vibrational characteristics of two-dimensional granular assemblies

Two-dimensional disordered granular assemblies composed of 2048 polydispersed frictionless disks are simulated using the discrete element method. The height of the first peak of the pair correlation function, g1, the local and global gbond orientational parameters lψ6and ψ6, and the fluctuations of these parameters decrease with increasing polydispersity s,implying the transition from a polycrystalline state to an amorphous state in the system. As s increases, the peak position of the boson peak ωBP shifts towards a lower frequency and the intensity of the boson peak D(ωBP)/ωBP increases, indicating that the position and the strength of the boson peak are controlled by the polydispersity of the system. Moreover, the inverse of the boson peak intensity ωBP/D(ωBP), the shear modulus G, and the basin curvature SIS all have a similar dependence on s, implying that the s dependence of the vibrational density of states at low frequencies likely originates from the s dependence of the basin curvature.     

Relaxation dynamics and power spectra of liquid water: a molecular dynamics simulation study

We present molecular dynamics simulations of liquid water at normal and supercooled conditions. Autocorrelation functions (ACFs) of several structural quantities and their fourier transforms are obtained and analysed. Structural correlations and relaxation times increase linearly with degree of supercooling. Power spectra of ACFs show increase in librational motion of liquid water with cooling. These modes intensify with supercooling because of structuring and ordering of water molecules. Overall, liquid water structure is homogenous over the temperatures and pressures studied and undergoes fluctuation–dissipation in its local-density variations [English and Tse, Phys. Rev. Lett. 106, 037801 (2011)].     

Experimental study on age and gender differences in microscopic movement characteristics of students

Campus security has aroused many concerns from the whole society. Stampede is one of the most frequent and influential accidents in campus. Studies on pedestrian dynamics especially focusing on students are essential for campus security, which are helpful to improve facility design and emergency evacuation strategy. In this paper, primary and middle school students were recruited to participate in the single-file experiments. The microscopic movement characteristics,including walking speed, headway, gait characteristics(step length, step frequency and swaying amplitude) and their relations were investigated. Age and gender differences in the headway-speed diagram and space requirements were analyzed by statistical tests. The results indicated that the impacts of age and gender were significant. There were three stages for the influence of gender on the headway-speed diagram for both age groups. The impacts on students' space requirements were consistent for different age and gender groups. But the impacts of age and gender on free-flow speed were affected by each other. Due to the connection of walking speed and gait characteristics, the comparisons of gait characteristics between different ages and genders were performed to understand the corresponding differences in speed more deeply. The results showed that differences in step length and swaying amplitude between males and females were significant for both age groups. The effect of gender on step frequency was significant for primary students. But for middle school students,whether gender had significant impact on step frequency was not clear here because of the large P-value. Besides, the influence of age on gait characteristics changed with gender.     

A first-principles study on the structural, lattice dynamical and thermodynamic properties of beryllium chalcogenides

First-principles calculations, which are based on the plane-wave pseudopotential approach to the density functional theory and the density functional perturbation theory within the local density approximation, have been performed to investigate the structural, lattice dynamical and thermodynamic properties of zinc blende (B3) structure beryllium chalcogenides: BeS, BeSe and BeTe. The results of ground-state parameters and phonon dispersion are compared and contrasted with the experimental and theoretical data of previous literature. The phonon frequencies at the zone-center are analyzed. We also used the phonon density of states and quasiharmonic approximation to calculate and predict some thermodynamic properties such as entropy, heat capacity, internal energy and free energy of the B3 phase beryllium chalcogenides.     

空调热水一体机结霜工况下运行特性的模拟研究

针对传统建模方法的局限性,采用人工神经网络对冬季结霜工况下空调热水一体机的动态运行特性进行了模拟研究,利用BP算法对网络的各层连接权值进行学习和调整,建立了机组运行特性预测模型;采用期望偏差百分率(EEPk)进行误差分析,其计算结果表明网络的预测效果与训练效果吻合较好,证明该方法切实可行,为更好的分析空调热水一体机的性能提供一种思路,同时也为机组的除霜控制和在线故障诊断提供了参考。